Displacement based fragility curves for R.C.C. frame structures in context of Dhaka, Bangladesh.

In recent past, severe earthquakes have caused substantial physical losses and casualties in this sub-continent. At present Bangladesh is in high risk of attacked by earthquakes. Since a majority of the population is living in earthquake-prone areas, it is probable that such terrible events will take place again in the near future. Moreover, it is not easy to cope with the substantial direct and indirect economical losses after each devastating earthquake for a developing country like Bangladesh. Because in this country most of the reinforced concrete buildings are not designed according to the current building code, seismic behavior is not taken into consideration in the architectural design and during selection of the structural system and supervision in the construction phase is not adequate which in turn induces deficiencies like poor concrete quality, inadequate detailing of reinforcement etc. It is, therefore, vital to quantify the earthquake risk and to develop strategies for disaster mitigation. In order to achieve this goal, an extensive and inter-disciplinary study is required. Such a study is composed of two parts: hazard determination and vulnerability assessment. This study describes the methods by which it is possible to determine the vulnerability of existing engineering structures and building stock. The tool that is employed to assess the seismic performance of reinforced concrete frame structures is the fragility curve. By definition, fragility curves provide estimates for the probabilities of reaching or exceeding various limit states at given levels of ground shaking intensity for an individual structure or population of structures (MAE Report, 2003). A limit state; which is in the same terms as the response, usually represents a damage condition or a limitation of usage. The primary focus of this paper is to present a proper methodology that can be followed to construct fragility curves for R.C.C frame structures in Bangladesh and to generate fragility curves for some specific type of RCC frame structures using this methodology

Effect of Carbon Nanotube Size on Compressive Strengths of Nanotube Reinforced Cementitious Composites

Application of nanoscale science to construction material has already begun. In recent times, various nanofibers have raised the interest of researchers due to their exceptional mechanical properties and high potential to be used as reinforcement within cement matrix. Carbon nanotube (CNT) is one of the most important areas of research in the field of nanotechnology. The size and exceptional mechanical properties of CNT show their high potential to be used to produce high performance next generation cementitious composites. In this study, an attempt has been made to investigate the effect of size of CNTs on compressive strengths of CNT reinforced cement composites. Seven different sizes of multiwalled nanotubes (MWNTs) were used to produce MWNT-cement composites. A trend was observed regarding the effect of nanotube size on compressive strength of composites in most cases. MWNT with outside diameter (OD) of 20 nm or less exhibited relatively better performance. Smaller MWNT can be distributed at much finer scale and consequently filling the nanopore space within the cement matrix more efficiently. This in turn resulted in stronger composites

Suitability of locally manufactured galvanized iron (GI) wire fiber as reinforcing fiber in brick chip concrete

A case study has been conducted in order to improve concrete quality in Bangladesh, using fiber reinforcing techniques with locally available low-cost Galvanized Iron (GI) wire fibers. GI wire is in fact mild steel wire with a thin coating of zinc. In order to assess the suitability of GI wire fibers as an alternative to steel fibers, various properties of GI wire fibers i.e. tensile strength, bending capacity etc. have been investigated and compared with the properties of steel fibers in light of relevant ACI and ASTM guidelines. Various tests were conducted on GI wire fibers as well as plain concrete reinforced with GI wire fibers. The experimental results show that GI wire fiber has compatible properties with steel fibers. Moreover, compressive strength, flexural strength, toughness indices and residual strength factors of GI wire fiber reinforced concrete (GFRC) have shown significant improvement compared to normal concrete. A comparison with Steel Fiber Reinforced Concrete (SFRC) revealed that performance of GFRC is quite similar to that of SFRC. It was observed that fiber content of 2.5-3.5% by weight produces relatively better results for the particular mix design used in the study. Furthermore, a cost analysis reveals that SFRC is about 19% more expensive than GFRC in Bangladesh; for 1 cubic meter of concrete work when fiber dosage is 2.5% by weight. Therefore, the study finds that GFRC has shown some promising results to be a low-cost alternative to steel fiber reinforced concrete from Bangladesh’s perspective

Measurement of Surface Damage through Boundary Detection: An Approach to Assess Durability of Cementitious Composites under Tannery Wastewater

Concrete structures are often subjected to aggressive aqueous environments which consist of several chemical agents that can react with concrete to produce adverse effects. A Central Effluent Treatment Plant consisting of reinforced concrete structures which is being constructed at Savar, Bangladesh, is an example of such a case. The purpose of this treatment facility is to reduce the environmental pollution created by tannery wastewater. However, tannery wastewater consists of several chemicals such as sulfates, chlorides, and ammonium, which, from the literature, are known to generate detrimental effects on concrete. Evaluation of durability of concrete structures in such environments is therefore imperative. This paper highlights a technique of boundary detection developed through image processing performed using MATLAB. Cement mortar cubes were submerged in simulated tannery wastewater and the images of the surface of cubes were taken at several time intervals. In addition, readings for compressive strength and weight were also taken on the same days. In this paper, an attempt is made to correlate the results from image processing with that of strength and weight loss. It was found, within the scope of this study, that the specimens which suffered greater strength and weight loss also underwent greater loss of surface area

Optimum Proportion of Masonry Chip Aggregate for Internally Cured Concrete

Abstract Proper curing of concrete is essential for achieving desirable mechanical properties. However, in a developing country like Bangladesh, curing is often neglected due to lack of proper knowledge and skill of local contractors. Consequently, general concreting work of the country has been found to have both strength and durability issues. Under such scenario, internal curing could be adopted using masonry chip aggregate (MCA) which is quite common in this region. It is observed that saturated MCA desorbs water under favorable relative humidity and temperature. This paper presents the effectiveness of MCA as internal curing medium and recommends a tentative optimum mix proportion to produce such concrete. The experimental study was conducted in two phases. It was found that 20% replacement of stone chips with MCA produced better performing internally cured concrete both in terms of strength and durability. Performance of internally cured concrete with recommended proportion of MCA is comparable to that of normally cured control concrete samples with conventional stone chips. In addition, internally cured concrete performed significantly better than control samples when kept under similar adverse curing conditions. In the absence of supply of external water for curing, compressive strength of internally cured concrete for 20% replacement can be as high as 1.5 times the strength of the control concrete samples. Significant better performance in permeability than that of control samples was also observed for this percent replacement under such adverse curing conditions

Air Quality Dispersion Modelling to Evaluate CIPP Installation Styrene Emissions

Cured-in-place pipe (CIPP) is one of the most popular in situ rehabilitation techniques to repair sewer and water pipes. While there are multiple approaches to curing CIPP, steam-curing of styrene-based resins has been found to be associated with air-borne chemical emissions. Health officials, utilities and industry representatives have recognized the need to know more about these emissions, especially styrene. Such concern has led to multiple studies investigating the concentrations of volatile organic compounds on CIPP installation sites. This study expands upon previous effort by modeling worst-case, steam-cured CIPP emissions over a 5-year weather record. The effort also includes calibration of the model to emissions averages over the work day rather than instantaneous field measurements. Dispersion modelling software, AERMOD, was utilized to model the styrene component of CIPP emissions on two CIPP installation sites in the US. Based on the analysis results, it was found that the styrene emitted from stacks dissipates rapidly with styrene concentrations only exceeding minimum health and safety threshold levels at distances close to the stack (2 m or less). The values predicted by the model analysis are comparable with the field measured styrene concentrations from other studies. Current safety guidelines in the US recommend a 4.6-m (15-ft) safety perimeter for stack emission points. The results of this study indicate that significant and lasting health impacts are unlikely outside recommended safety perimeter. The results also validate the importance of enforcing recommended safety guidance on steam-cured CIPP sites